This invention relates to a single stage process for the preparation of polyamines containing primary amino groups. This invention also relates to the use of the polyamines according to the invention for the production of polyurethane(urea)s.
It is known that isocyanates can be converted into amines by acid or basic catalysis. Such processes are described in "The Organic Chemistry of Nitrogen" by N.V. Sidgwick, Clarendon Press, Oxford, page 236 (1966) and in "Advanced Organic Chemistry: Reactions, Mechanisms and Structure" by J. March, McGraw-Hill Book Co., New York, page 658 (1968). Sidgwick mentions the possibility of hydrolyzing isocyanate groups by alkaline hydrolysis, but only in non-specific and general terms.
Multi-stage hydrolysis processes (DE-A-No. 2,948,419, DE-AS No. 3,039,600, DE-SO No. 3.131,252) as well as single stage processes (3,223,400 EP No. -97,299, DE-OS No. 3,223,398/EP No.-97,298 and DE-OS No. 3,223,397/EP No. -97,290) have been disclosed. In the single stage hydrolysis process of DE-OS No. 3,223,400, "etherial solvents" are used together with tertiary amines as catalysts. DE-OS No. 3,223,398 discloses a process in which polar solvents such as dimethylformamide are used together with tertiary amines or relatively large quantities of alkali metal hydroxides, alkali metal silicates or alkali metal cyanides as catalysts. Polar solvents are used together with carbonates or carboxylates as catalysts in the process disclosed in DE-OS No. 3,223,397.
The known processes for the preparation of polyamines are all relatively complicated. Even in the known single stage processes further simplication resulting in the production of polyamines even more economically and with even better conversion rates of NCO/NH.sub.2 (i.e. higher NH.sub.2 numbers) by even smoother reactions would be advantageous. It would be desirable to have a process with the following advantageous features: (a) no filtration required; (b) no distillative separation of a tertiary amine catalyst required; and (c) drastic reduction in the quantity of catalyst required so that the catalyst may be left in the polyamine.
It would also be desirable to obtain as far as possible quantitative conversion of NCO groups into NH.sub.2 groups (high conversion rates of NCO/NH.sub.2 to yield a high amine number close to the theoretical value) as well as: (a) very low proportion of monomeric amines; (b) no formation of by-products which must be removed; and (c) the ability to work up the polyamines and auxiliary substances by simple methods.
A process leading to end products which contain only a very small proportion of low molecular weight diamines or polyamines would be advantageous.
It is desirable for various reasons to reduce the proportion of monomeric amine in the relatively high molecular weight amino polyethers and amino polyesters as far as possible. Reduced monomeric amine results in reduced physiological risk, reduction of the well known deleterious effect of free aromatic low molecular weight amines on the resistance of amino polyethers or esters and of the polyurethanes produced from them to light and discoloration and enables consistent production of polyurethane products with reproducible properties.
One possible method for keeping the monomeric amine content (e.g. the TDA content) in the high molecular weight polyamine(s) very low is to reduce the monomeric low molecular weight isocyanate content (e.g. TDI content) in the corresponding isocyanate prepolymer(s) before hydrolysis. Such reduction may be accomplished by thin layer evaporation or distillation. These methods are, however, expensive and complicated.
In another approach to obtaining an end product containing only a low proportion of low molecular weight amine, a sub-equivalent quantity of diisocyanate (based on the "ideal" isocyanate prepolymer (NCO/OH ratio 2:1)) in the preparation of the prepolymer is used. The disadvantage of this method is that both the isocyanate prepolymer and the end product are relatively high viscosity substances which would be difficult to work up.
In DOS No. 3,437,632 it is proposed to lower the monomeric, low molecular weight amine content by selective reaction with mono-, di- and/or polyisocyanates (e.g. propyl isocyanates). This also results in a considerable increase in viscosity.
Lastly, the use of minor quantities of "H-active" compound in the preparation of the isocyanate preliminary products is recommended in DOS No. 3,223,397. Here again, a considerable increase in viscosity occurs in the end product.